Aluminum Sandwich Panels (also known as aluminum composite materials ACM) are used in architectural applications, such as to cover the outside surface of buildings (façade). ACM are widely used in countries in Europe, Middle East and parts of the former Soviet Union. ACM typically consist of two aluminum panels, (i.e., sheets or layers), with a usual thickness of about 0.5 mm, and a polymer core composition between the panels containing flame retardants, and having a usual thickness of about 3 mm. Normally, these ACM are produced via extrusion and calendaring. In Europe, they have to comply with regulations relevant for construction, such as the important fire safety construction product regulations (CPR). Depending on the height of the building, either Euroclass B (for buildings up to 20 m tall) or Euroclass A2 (for buildings taller than 20 m) regulations need to be passed.
Euroclass B panels have to pass the SBI test. This test is conducted in a room in which the samples (1.0×1.5 m+0.5×1.5 m) are mounted in a 90° angle and exposed to a gas burner flame. The fire growth rate (FIGRA) needs to be max 120 W/s and the total heat released (THR 600s) has to be max 7.5 MJ. Besides the SBI test, EN 11925-2 also needs to be passed with a flame spread max 150 mm within 60 seconds. The Euroclass B fire safety test is typically easy to achieve. To meet these requirements, aluminum hydroxide (ATH) can be utilized as flame retardant in polymer composition with a loading of around 70-75% by weight ATH.
The Euroclass A2 fire safety test is more difficult to achieve. Although Euroclass A2 panels also must be able to pass the SBI test, and have the same limits as Euroclass B panels, the more demanding hurdle is the bomb calorimeter test according to EN ISO 1716 entitled “Reaction to fire tests for building and transport products—Determination of heat of combustion”. The polymer core material has to have a calorific potential (PCS) of max 3.0 MJ/kg. That typically means a polymer or organic content of 10 wt % max, and an inorganic flame retardant loading of over 90 wt %. As disclosed in EP 2420380 A1, these high inorganic loadings cannot be extruded and thus cannot use the existing extrusion/calendaring systems used in the industry. One must use an alternative system, such as the compression molding technology described in EP 2420380 A1. This is a distinct disadvantage since the cost is high for installing new equipment.
Accordingly, there is a need to formulate polymeric core compositions for ACM having over 90 wt % inorganic flame retardants such that the compositions can be extruded and are able to pass the Euroclass A2 fire safety tests.